Synchronous semiconductor device, and inspection system and method for the same

ABSTRACT

The present invention provides a synchronous semiconductor device suitable for improving the efficiency of application of electrical stresses to the device, an inspection system and an inspection method thereof in order to efficiently carrying out a burn-in stress test. A command latch circuit having an access command input will output a low-level pulse in synchronism with an external clock. The pulse will pass through a NAND gate of test mode sequence circuit and a common NAND gate to output a low-level internal precharge signal, which will reset a word line activating signal from the control circuit. Simultaneously, an internal precharge signal passing through the NAND gate will be delayed by an internal timer a predetermined period of time to output through the NAND gate a low-level internal active signal, which will set a word line activating signal from the control circuit.

This is a division of application Ser. No. 09/820,715 filed Mar. 30,2001, now U.S. Pat. No. 6,559,669, the disclosure of which is herebyincorporated by reference herein in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a synchronous semiconductor device andan inspection system for synchronous semiconductor devices, and moreparticularly to a synchronous semiconductor device and an inspectionsystem for synchronous semiconductor device, incorporating a function toeffectively perform burn-in stress test for screening defectiveproducts.

2. Description of the Prior Art

Any residual ionized movable impurity in the oxide of a semiconductordevice may lead in practice to a permanent defective such as degeneratedcapacity to voltage and short circuit between wirings due to thedisplacement of such impurity caused by thermal or electric stresses. Inorder to eliminate these potentially problematic devices as defectivesfrom final products prior to shipping, a burn-in stress test isperformed. The burn-in stress test consists of a screening test byapplying thermal and electric stresses to the subject.

The burn-in stress test is performed on the synchronous semiconductorsin a similar manner. The synchronous semiconductors execute its internaloperation in synchronism with an external clock. In order to applyelectric stresses to the inside device, the operation is to beconfigured at the rate of the external clock.

For example, in a synchronous dynamic random access memory (referred toas SDRAM herein below), electric stresses will be at maximum when a wordline is selected and a voltage more risen to the power supply voltage isapplied to the gate of a MOS transistor. In order to apply to the entiredevice some electrical stresses, the selected word line has to besequentially changed. Although by the demand of high-speed operation inthese days a next generation SDRAM has been developed which enablesaccelerated cyclic operation by performing a series of data accesses inone command input, the burn-in stress test is indispensable for suchproducts.

The prior art technology with respect to the ordinary SDRAM will bedescribed by referring to the controller circuit of word lines shown inFIG. 10, and operating waveforms in FIG. 11. In the art, a controlcommand CMD and a precharging command PRE_CMD may be input synchronouslyat the rising edge of an external clock CLK. A latch 110, 110 in acommand latch circuit 100, 100 accepts the external clock CLK at aninput and at the other input the output from a NAND circuit 130, 130that receives the commands CMD and PRE_CMD and the external clock CLK,CLK. When the external clock CLK, CLK goes to high if either the controlcommand CMD or the precharging command PRE_CMD is high then this commandstatus will be latched. A one-shot trigger circuit 120, 120 in thefollowing stage will be triggered by the transition of the output of thelatch 110, 110 to low when latching so as to output a low-level pulsesignal having the width determined by a series of inverters of oddstages (only three stages shown in FIG. 10). The pulse signal means aninternal active signal ACTV, or an internal precharge signal PRE, whichwill set and reset the activating signal WL of word lines by repeatedlysetting and resetting the latch 210 in the controller circuit 200alternately and in synchronism with the rising edge of the externalclock CLK, CLK. When resetting, the word line next to the one currentlyselected will be selected such that electrical stress will be appliedsequentially through the device thoroughly.

Another prior art technology with respect to the next generation SDRAMwill be described by referring to a controller circuit of word linesshown in FIG. 12 and to operating waveforms shown in FIG. 13. In thisprior art, a circuit block 100 identical to the command latch circuit100, 100 shown in FIG. 10 is implemented so as to accept the controlcommand CMD synchronously input at the rising edge of an external clockCLK. A following one-shot trigger circuit 120 at the next stage willoutput a predetermined pulse at low-level. This low-level pulse is aninternal active signal ACTV, which will be input to the controllercircuit 200 to output to the word line activating signal WL.

The internal active signal ACTV is also input to an internal timercircuit 300. The internal timer circuit 300 can be composed of invertersof even stages as shown in FIG. 12, and may be composed of anyarrangements which measure the given time t1. When the given time t1elapses, the circuit outputs a low-level pulse signal for an internalprecharge signal PRE to reset the latch 210 in the controller circuit200 to deactivate the word line activating signal WL. Since in this nextgeneration SDRAM, one command input causes a series of data accesses tobe performed, the internal precharge signal PRE will be automaticallyissued after elapsing the given time t1 configured by the internal timercircuit 300 based on the internal active signal ACTV.

The word line activating signal WL activates the word line correspondingto a row address selected by the circuit not shown in the figure toapply electric stress during the given time t1 configured by theinternal timer circuit 300. At the end of the given time t1, theactivated word line will be deactivated and a next word line will beset. Then the identical operation will be iteratively repeated at therising edge of the external clock CLK in order to apply the electricalstress to the entire device.

However, in the ordinary SDRAM as stated above, the activated period andprecharging period of a word line will be iteratively repeated in analternate manner for each cycle of the external clock CLK. Thus theperiod of time in which the electrical stress is applied to the deviceafter activation of the word line will be one half of the net testingperiod. This indicates that a test that can apply the electrical stressmore effective than this percentage is not achievable and that anyattempts to further saving time of test may fail.

In addition, the next generation SDRAM as described above is required tooperate at the external clock CLK of high frequency, on the demand ofaccelerated operation. The given time t1 to be measured by the internaltimer circuit 300 will then be set to a shorter period of timeappropriate to the power of data accessing operation. In the burn-instress test on the other hand, the maximum performance may not beachieved by the limitation in the testing environment and the like, thusin general the synchronous semiconductor device has enough margins tooperate with respect to the frequency of the external clock CLK used inthe test. This concludes that the electrical stress may not effectivelyapplied because of the small duty rate in the given time t1 that theword lines are activated.

SUMMARY OF THE INVENTION

The present invention has been made in view of the above circumstancesand has an object to effectively perform the burn-in stress test and toprovide a synchronous semiconductor device having a higher efficiencyfor applying electrical stress to the devices and an inspection systemthereof.

In order to achieve the above object, the synchronous semiconductordevice in accordance with one aspect of the present invention, whichiteratively repeats the alternate transits between an activated stateand an inactivated state for performing a test in the activated state,comprises, a latch unit for latching a synchronous activating signal insynchronism with a first synchronizing timing of a synchronizing signal;an inactivating signal detector unit for detecting an inactivatingsignal a predetermined period of time before the activated state, and aninactivating unit for commanding an inactivated state based on theinactivating signal thus detected.

The synchronous semiconductor device may use the inactivating signaldetector unit to detect the inactivating signal a predetermined periodof time before going to an activated state, at the time when performinga test in the activated state while iteratively repeating the transit ofoperating states between activated and inactivated states in analternate manner to command by the inactivating unit to go toinactivated state prior to latching by the latch unit the synchronousactivating signal in synchronism with the first synchronizing timing ofthe synchronizing signal in order to go to the activated state.

The inactivated state maybe thereby configured a predetermined period oftime before the first synchronizing timing of the synchronizing signalto go to the activated state. The duration of the activated state duringthe test may be arbitrarily set by using the synchronous activatingsignal that synchronizes with the synchronizing signal in the normaloperation of the synchronous semiconductor device. Therefore theactivated state needed during the test may be effectively configured.The testing period may be shortened by increasing the rate of durationof the activated state.

A synchronous semiconductor device in accordance with another aspect ofthe present invention, which alternately transits between an activatedstate and an inactivated state in an iterative manner for performing atest in the activated state, comprises, a latch unit for latching asynchronous inactivating signal in synchronism with a firstsynchronizing timing of a synchronizing signal; an activating signaldetector unit for detecting an activating signal a predetermined periodof time after the inactivated state, and an activating unit forcommanding an activated state based on the activating signal thusdetected.

The synchronous semiconductor device as stated above may use the latchunit to latch the synchronous inactivating signal in synchronism withthe first synchronizing timing of the synchronizing signal to go to theinactivated state at the time when performing a test in the activatedstate while iteratively repeating the operating states between activatedand inactivated states in an alternate manner, then, may use, after apredetermined period of time, the activating signal detecting unit todetect the activating signal to go to the activated state.

The activated state may be thereby configured a predetermined period oftime after the first synchronizing timing of the synchronizing signal togo to the inactivated state. The duration of the activated state duringthe test may be arbitrarily set by using the synchronous inactivatingsignal that synchronizes with the synchronizing signal in the normaloperation of the synchronous semiconductor device. Therefore theactivated state needed during the test may be effectively configured.The testing period may be shortened by increasing the rate of durationof the activated state.

An inspection system for the synchronous semiconductor device inaccordance with one aspect of the present invention, which iterativelyrepeats the transits between an activated state and an inactivated statein an alternate manner for performing a test in the activated state,comprises, a synchronization signal supplying unit for supplying asynchronization signal to a synchronous semiconductor device; asynchronous activating signal supplying unit for supplying a synchronousactivating signal in synchronism with the first synchronizing timing ofthe synchronization signal; and an inactivating signal supplying unitfor supplying an inactivating signal a predetermined period of timebefore an activated state.

The inspection system of the synchronous semiconductor device inaccordance with the present invention may use the synchronization signalsupplying unit to supply the synchronization signal and use theinactivating signal supplying unit to supply the inactivating signal apredetermined period of time before an activated state, at the time whenperforming a test in the activated state while iteratively repeating thetransit of operating states between activated and inactivated states inan alternate manner. Thereafter the system may use the synchronousactivating signal supplying unit to supply the synchronous activatingsignal in synchronism with the first synchronizing timing of thesynchronization signal.

The inactivating signal may be supplied thereby a predetermined periodof time before the first synchronizing timing of the synchronizationsignal to go to the activated state, so that the duration of theactivated state of the synchronous semiconductor device during the testmay be arbitrarily configured while supplying the synchronization signalas well as the synchronization activating signal for synchronizingtherewith in the normal operation of the synchronous semiconductordevice. Therefore an inspection system may be provided in which theactivated state needed during the test may be effectively configured andthe testing period may be shortened by increasing the rate of durationof the activated state.

An inspection system for the synchronous semiconductor device inaccordance with another aspect of the present invention, whichiteratively repeats the transits between an activated state and aninactivated state in an alternate manner for performing a test in theactivated state, comprises, a synchronization signal supplying unit forsupplying a synchronization signal to a synchronous semiconductordevice; a synchronous inactivating signal supplying unit for supplying asynchronous inactivating signal in synchronism with the firstsynchronizing timing of the synchronization signal; and an activatingsignal supplying unit for supplying an activating signal a predeterminedperiod of time after an inactivated state.

The inspection system of the synchronous semiconductor device inaccordance with the present invention may use the synchronization signalsupplying unit to supply the synchronization signal and use thesynchronous inactivating signal supplying unit to supply thesynchronization inactivating signal in synchronism with the firstsynchronizing timing of the synchronization signal, at the time whenperforming a test in the activated state while iteratively repeating thetransit of operating states between activated and inactivated states inan alternate manner. After a predetermined period of time, the systemmay use the activating signal supplying unit to supply the activatingsignal.

The activating signal may be supplied thereby a predetermined period oftime after the first synchronizing timing of the synchronization signalto go to the inactivated state, so that the duration of the activatedstate of the synchronous semiconductor device during the test may bearbitrarily configured while supplying the synchronization signal aswell as the synchronization inactivating signal for synchronizingtherewith in the normal operation of the synchronous semiconductordevice. Therefore an inspection system may be provided in which theactivated state needed during the test may be effectively configured andthe testing period may be shortened by increasing the rate of durationof the activated state.

An inspection method in accordance with one aspect of the presentinvention for inspecting the synchronous semiconductor device, whichiteratively repeats the transits between an activated state and aninactivated state in an alternate manner for performing a test in theactivated state, comprises the steps of a predetermined period of timeprior to going to the activated state, detecting an inactivating signal;transiting to the inactivated state; latching thereafter asynchronization activating signal in synchronism with the firstsynchronizing timing of a synchronization signal to go to an activatedstate.

In accordance with the inspection method of the synchronoussemiconductor device, which iteratively repeats the alternate transitsbetween an activated state and an inactivated state for performing atest in the activated state, which device transits to the inactivatedstate by an inactivating signal a predetermined period of time beforegoing to an activated state and then latches a synchronizationactivating signal in synchronism with the first synchronization timingof the synchronization signal to go to the activated state, the timingof the inactivating signal may be arbitrarily configured so that thetesting period may be shortened by increasing the rate of duration ofthe activated state while making use of the synchronization activatingsignal in synchronism with the synchronization signal in the normaloperation of the synchronous semiconductor device.

An inspection method in accordance with another aspect of the presentinvention for inspecting the synchronous semiconductor device, whichiteratively repeats the transits between an activated state and aninactivated state in an alternate manner for performing a test in theactivated state, comprises the steps of: latching a synchronizationinactivating signal in synchronism with the first synchronizing timingof a synchronization signal to transit to an inactivated state; and apredetermined period of time after the inactivated state, detecting anactivating signal to go to the activated state.

In accordance with the inspecting method of the synchronoussemiconductor device, which device transits to the activated state by anactivating signal a predetermined period of time after transiting to theinactivated state by an synchronization inactivating signal insynchronism with the first synchronization timing of the synchronizationsignal at the time when performing a test in the activated state whileiteratively repeating the transit of operating states between activatedand inactivated states in an alternate manner, the timing of theactivating signal may be arbitrarily configured so that the testingperiod may be shortened by increasing the rate of duration of theactivated state while making use of the synchronization inactivatingsignal in synchronism with the synchronization signal in the normaloperation of the synchronous semiconductor device.

The above and further objects and novel features of the invention willmore fully appear from following detailed description when the same isread in connection with the accompanying drawings. It is to be expresslyunderstood, however, that the drawings are purpose of illustration onlyand not intended as a definition of the limits of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of this specification illustrate an embodiment of the inventionand, together with the description, serve to explain the objects,advantages and principles of the invention. In the drawings,

FIG. 1 is a schematic block diagram of a circuit in accordance withfirst preferred embodiment of the present invention;

FIG. 2 is a schematic circuit diagram depicting a controller circuit ofword lines in accordance with the first preferred embodiment of thepresent invention;

FIG. 3 is a schematic waveform diagram illustrating the operatingwaveforms in accordance with the first preferred embodiment of thepresent invention;

FIG. 4 is a schematic block diagram of a circuit in accordance withsecond preferred embodiment of the present invention;

FIG. 5 is a schematic circuit diagram depicting a controller circuit ofword lines in accordance with the second preferred embodiment of thepresent invention;

FIG. 6 is a schematic waveform diagram illustrating the operatingwaveforms in accordance with the second preferred embodiment of thepresent invention;

FIG. 7 is a schematic block diagram of a circuit in accordance withthird preferred embodiment of the present invention;

FIG. 8 is a schematic circuit diagram depicting a controller circuit ofword lines in accordance with the third preferred embodiment of thepresent invention;

FIG. 9 is a schematic waveform diagram illustrating the operatingwaveforms in accordance with the third preferred embodiment of thepresent invention;

FIG. 10 is a schematic circuit diagram depicting a controller circuit ofword lines in accordance with a Prior Art;

FIG. 11 is a schematic waveform diagram illustrating the operatingwaveforms in accordance with the Prior Art;

FIG. 12 is another schematic circuit diagram depicting a controllercircuit of word lines in accordance with another Prior Art; and

FIG. 13 is another schematic waveform diagram illustrating the operatingwaveforms in accordance with another Prior Art.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A detailed description of first through third preferred embodimentsembodying the synchronous semiconductor device and the inspection methodof synchronous semiconductor device in accordance with the presentinvention will now be given in greater details referring to theaccompanying drawings.

In the preferred embodiments disclosed herein, the detailed descriptionwill be given by way of example in case in which a next generation SDRAMthat executes a series of data access operations by one command input issubject to a burn-in stress test. Now referring to FIG. 1, there isshown a schematic block diagram of a circuitry in accordance with firstpreferred embodiment. FIG. 2 shows a schematic circuit diagram depictinga controller circuit of word lines in accordance with the firstpreferred embodiment. FIG. 3 is a schematic waveform diagramillustrating the operating waveforms in accordance with the firstpreferred embodiment. FIG. 4 is a schematic block diagram of a circuitin accordance with second preferred embodiment. FIG. 5 is a schematiccircuit diagram depicting a controller circuit of word lines inaccordance with the second preferred embodiment. FIG. 6 is a schematicwaveform diagram illustrating the operating waveforms in accordance withthe second preferred embodiment. FIG. 7 is a schematic block diagram ofa circuit in accordance with third preferred embodiment. FIG. 8 is aschematic circuit diagram depicting a controller circuit of word linesin accordance with the third preferred embodiment. FIG. 9 is a schematicwaveform diagram illustrating the operating waveforms in accordance withthe third preferred embodiment. The similar members to those used in thePrior Art are designated to the identical reference numbers and thedetailed description of the parts will be omitted.

In the circuit block diagram of first preferred embodiment shown in FIG.1 includes two groups of circuits, namely, a test mode sequence circuit10 and a user mode sequence circuit 400, as the circuits for performingaccessing operation in one cycle composed of an activated state and aninactivated state, in the next generation SDRAM. The term “activated”state indicates a period in which a word line applied with a raisedvoltage for accessing the memory cell is input to the gate of switchingMOS transistor in the memory cell, and that the field in the oxide ofthe gate is subject to the most severe electrical stress in the SDRAM.The term “inactivated” state indicates a period in which bit lines aftermemory access is precharged and that the configuration of selected wordline is performed by changing row address for use in the next activatedstate.

The two groups of circuits including the test mode sequence circuit 10and the user mode sequence circuit 400 are those operating the access inthe normal use as well as in the burn-in stress test. In the nextgeneration SDRAM, the user mode sequence circuit 400 has to operate witha cycling time of tenths nanoseconds in order to achieve a high-speedaccess in the normal use. On the other hand, because of limitations inthe burn-in stress test, which will be conducted under a raisedtemperature along with a number of synchronous semiconductor devices tobe tested at the same time, it is not possible to reduce the cyclingtime in the test mode sequence circuit 10.

Thus, in the user mode sequence circuit 400 the ACTV circuit requiredfor the access operation will be served in advance, followed by a PREcircuit that precharges after the completion of access so as to reducethe duration of cycling time. In the test mode sequence circuit 10, incontrast, since the rate of the duration of active state needs to beextended for performing an effective burn-in stress test, the PREcircuit that precharges in the minimum inactivated state necessary willbe operated prior to the ACTV circuit that performs an access in theactivated state.

Switching between the test mode sequence circuit 10 and the user modesequence circuit 400 will be performed by a test mode discriminatorcircuit 60 to which a test mode input signal TTST is fed. Based on theconfiguration set in the test mode discriminator circuit 60, the testmode sequence circuit 10 or the user mode sequence circuit 400 will beoperated in correspondence with the control command CMD latched in thecommand latch circuit 100 in synchronism with the external clock CLK. Inthis context the control command CMD may be the own signal input throughan external terminal or a command converted by an circuit such asinternal command decoder from the signal input from one or more ofexternal terminals.

In the typical example of word line controller circuit as shown in FIG.2 in accordance with the present embodiment, the test mode sequencecircuit 10 includes two NAND gates 11 and 12, and an internal timer 13to which the output signals from the NAND gate 12 will be supplied. Theuser mode sequence circuit 400 in a similar way includes two NAND gates71 and 72, and an internal timer 73 to which the output signals of theNAND gate 72 will be fed. The output signals from the test mode sequencecircuit 10 and the user mode sequence circuit 400 will be reassembled inrespective NAND gates 74 and 75 for each of active signals and prechargesignals. The output signal of the NAND gate 74 will be used as theinternal active signal ACTV and the output signal of the NAND gate 75will be used as the internal precharge signal PRE, both signals beinginput to the controller circuit 200 in the next stage to set and resetthe word line activating signal WL.

A signal in phase with the test mode input signal TTST, output from abuffer 61 of the test mode discriminator circuit 60, will be input tothe NAND gates 11 and 12 to operate the test mode sequence circuit 10 inthe burn-in stress test. On the other hand, a signal opposite phase withthe test mode input signal TTST, output through the inverter 62 of thetest mode discriminator circuit 60, will be input to the NAND gates 71and 72 to operate the user mode sequence circuit 400 in case of normaloperation. In addition, a low-level pulse signal on the basis of thecontrol command CMD latched in synchronism with the external clock CLKat the command latch circuit 100 will be input to the NAND gates 11, 71and 72. To the NAND gate 12 input is the internal precharge signal PRE.

The operation of the controller circuit shown in FIG. 2 will bedescribed now with reference to the operational waveforms shown in FIG.3, which illustrates the waveforms in the burn-in stress test, or inother words the waveform when the test mode sequence circuit 10 is inservice. When an accessing command READ_CMD is supplied to the commandlatch circuit 100 as a control command CMD, the command latch circuit100 then will output a low-level pulse in synchronism with the externalclock CLK. This low-level pulse signal, which will be fed to the NANDgates 11, 71 and 72, will be accepted only by the NAND gate 11 of thetest mode sequence circuit 10 because the test mode input signal TTST isactive (i.e., high-level). The low-level pulse will be inverted in theNAND gate 11 to a high-level pulse to be input to the NAND gate 75. Theoutput signal of the inverter 62 in the test mode discriminator circuit60 is set to low-level so that both the output signal from the NAND gate72 and the output level from the internal timer 73 will be fixed tohigh. The NAND gate 75 then will output a low-level internal prechargesignal PRE by inverting a high-level pulse to reset the word lineactivating signal WL through the controller circuit 200.

At the same time the internal precharge signal PRE will also be input tothe NAND gate 12, which will produce a high-level signal as output. Thishigh-level signal, which will be subjected to be delayed for tRP by theinternal timer 13, will be input to the NAND gate 74. The other inputsignal fed to the NAND gate is high-level, so that the output signalfrom the NAND gate 74 will be flipped to low-level. More specifically,The gate will output an internal active signal ACTV to reset the wordline activating signal WL through the controller circuit 200. Byappropriately configuring the working time tRP of the internal timer 13a word line can be activated after a minimum precharge period necessary,so that the electrical stress may be applied at the maximum rate of timein a burn-in stress test. Therefore a more effective burn-in stress testmay be carried out.

A predetermined period of time after a resetting interval of the wordline activating signal WL in an inactive state by the accessing commandREAD_CMD supplied as a control command CMD, a signal for setting a wordline activating interval, which indicates the active state, can begenerated on the basis of the accessing command READ_CMD or the signalitself in an synchronous semiconductor device, the next generationSDRAM. The input accessing command READ_CMD synchronized to the externalclock CLK in the normal operation of the next generation SDRAM allowsthe word line activating period in the burn-in stress test to be set toa predetermined period of time, in particular the word line activatedperiod required in the burn-in stress test to be set in a manner moreeffective than ever. An increased rate of duration of the word lineactivating period may therefore lead to a shorter time of test.

If the accessing command READ_CMD, which activates the word line in thenormal operation is input in a burn-in stress test, a reset interval ofthe word line activating signal WL will be placed for a predeterminedperiod of time prior to the activation of the word line. That is, it maybe sufficient to feed an accessing command READ_CMD in a burn-in stresstest in a way identical to that in the normal operation, allowing thecontrol signals to be common in the test as well as in the normaloperation, resulting in a simpler handling in the burn-in stress test.The fact that there will not be a specific control signal to be inputonly in the burn-in stress test will eliminate the necessity of acircuit dedicated for a test and of proprietary external terminals forthe test, allowing a minimal overhead of the test in the next generationSDRAM.

It is to be noted here that the command latch circuit 100 is a latchunit, the internal timer 13 is an activation detector unit, or a delayunit, the NAND gate 74 is an activating unit. Also, the external clockCLK is a synchronization signal, the rising edge of the signal CLK is afirst synchronization timing. In addition, the accessing commandREAD_CMD used as a control command CMD is a synchronization inactivatingsignal, or a synchronization activation signal in the normal operation.The output signal from the NAND gate 12 is an activating signal, or aninput signal to the delay unit according to fifth aspect.

In the normal operation, the test mode input signal TTST is low-leveland inactive so that the low-level pulse based on the accessing commandREAD_CMD will be accepted by the user mode sequence circuit 400. Inother words, the NAND gate 71 having a low-level pulse supplied willoutput a high-level pulse to output an internal active signal ACTVthrough the NAND gate 74 in order to set the word line activating signalWL. On the other hand, as the low-level pulse will be similarly input tothe NAND gate 72 at the same time, a high-level pulse will be appearedat the output of the NAND gate 72, which pulse will be delayed for aninterval t1 by the internal timer 73 to output an internal prechargesignal PRE to reset the word line activating signal WL. Since theinterval t1 will be measured in the device, only one accessing commandREAD_CMD may invoke a complete operation for one cycle.

Now second preferred embodiment of the present invention will bedescribed in greater details herein below. In the schematic blockdiagram of circuit shown in FIG. 4, the command latch circuit 100, testmode discriminator circuit 60, and user mode sequence circuit 410 willhave the same structure as the circuits described in the preceding firstpreferred embodiment. In the second embodiment, a precharge controllercircuit 30 is added thereto for inputting a precharge control signalTPRE in a burn-in stress test to a test mode sequence circuit 20 toinvoke a precharging operation.

A typical example of word line controller circuit in accordance with thesecond preferred embodiment in FIG. 5 includes a test mode sequencecircuit 20 comprised of only one NAND gate 21. The user mode sequencecircuit 410 is composed of one NAND gate 72 and a internal timer 73 toinput the output signals from the NAND gate 72. The output signals formthe test mode sequence circuit 20 and the user mode sequence circuit 410will be gathered in the NAND gate 75 for the precharging signals andwill be input to the controller circuit 200 as an internal prechargesignal PRE. Here, with regard to the activating signal, the outputsignal of the command latch circuit 100 will be input directly to thecontroller circuit 200 as the internal active signal ACTV.

The signal output from the buffer 61 of the test mode discriminatorcircuit 60 will be input to the NAND gate 21 as a signal in phase to thetest mode input signal TTST in order to operate the test mode sequencecircuit 20 in the burn-in stress test. The signal output from theinverter 62 of the test mode discriminator circuit 60 will be fed to theNAND gate 72 opposite phase to the test mode input signal TTST tooperate the user mode sequence circuit 410 in the normal operation. Inaddition, the output signal of the command latch circuit 100, which is alow-level pulse signal based on a control command CMD, will be input tothe controller circuit 200 directly as an internal active signal ACTV,as well as to the NAND gate 72 at the same time. To the NAND gate 21input is the precharge control signal TPRE through the prechargecontroller circuit 30.

The operation of the controller circuit shown in FIG. 5 will bedescribed by referring to waveforms shown in FIG. 6. FIG. 6 showswaveforms in the burn-in stress test, i.e., those when the test modesequence circuit 20 is in operation. The precharge control signal TPRE,a low-level pulse input prior to an accessing command READ_CMD as thecontrol command CMD, will pass through the NAND gate 21 and NAND gate 75to generate an internal precharge signal PRE to reset the word lineactivating signal WL through the controller circuit 200.

The accessing command READ_CMD in synchronism with an external clock CLKwill be input to the command latch circuit 100 at a predetermineddelayed time after a precharge control signal TPRE. The command will beforward to the controller circuit 200 as a low-level pulse signalindicating the internal active signal ACTV to set the word lineactivating signal WL.

More specifically, if the precharge control signal TPRE is set to beadvanced a predetermined and appropriate period of time with respect tothe external clock CLK served for a synchronization signal of theaccessing command READ_CMD, the resetting period of time of the wordline activating signal WL by the internal precharge signal PRE passingthrough the controller circuit 200 may be served as the minimumprecharging period necessary, while the period which follows may beserved for the word line activating period, allowing the electricalstress in a burn-in stress test to be applied at a maximum rate ofduration to achieve a more efficient burn-in stress test.

The reset interval of the word line activating signal WL in inactivestate may be set at an arbitrary timing by the precharge control signalTPRE in response to the external input signal from the proprietaryexternal terminal or an existing external terminal. That is, a resettinginterval of the word line activating signal WL may be configured at anarbitrarily predetermined period of time prior to a raising edge of theexternal clock CLK which forces to a word line activating period, theactive stage. While making use of the synchronization activating signalin synchronism with the external clock CLK in the normal operation of asynchronous semiconductor device that is the next generation SDRAM, theword line activating period in the test may be arbitrarily set, allowingthe word line activating period required in the burn-in stress test tobe configured in an effective way. This may increase the rate ofduration of the word line activation so as to shorten the period of thetest. In addition, the input timing of the precharge control signal TPREmay be readily adjusted for each test or during a test in an arbitrarymanner so as to always optimize the test efficiency.

Here it is to be noted that the command latch circuit 100 is a latchunit, the precharge controller circuit 30 and the NAND gate 21 areinactivating detector unit, the NAND gate 75 is an inactivating unit.Also the external clock CLK is a synchronization signal in, the risingedge thereof is the first synchronization timing. Furthermore, theaccessing command READ_CMD served as a control command CMD is thesynchronization activating signal. The precharge control signal TPRE isan inactivating signal, or a first asynchronous control signal.

In the normal operation, the test mode input signal TTST is low-level,and inactivated, so that the output of the NAND gate 21 of the test modesequence circuit 20 will be set to high-level, as a result the low-levelpulse following the accessing command READ_CMD will be accepted by theuser mode sequence circuit 410. In other words, the low-level pulse willbe served as an internal active signal ACTV to directly set the wordline activating signal WL. The pulse will be also input to the NAND gate72 at the same time, the output signal of the NAND gate 72 which will bea high-level pulse will be delayed for t1 by the internal timer 73 tooutput an internal precharge signal PRE to reset the word lineactivating signal WL. Since the interval t1 will be measured in thedevice, only one accessing command READ_CMD may invoke a completeoperation for one cycle.

Now a third preferred embodiment of the present invention will bedescribed in greater details herein below. The command latch circuit100, test mode discriminator circuit 60, user mode sequence circuit 410,and test mode sequence circuit 20 in the schematic block diagram ofcircuitry of FIG. 7 are identical to those described in the foregoingsecond preferred embodiment of the present invention. In the presentthird embodiment, a CLK falling edge detector circuit 40 and aprecharging controller circuit 50 are incorporated instead of theprecharge controller circuit 30 for inputting a precharging controlsignal TXPRE in synchronism with a falling edge of the external clockCLK to the test mode sequence circuit 20 to invoke a prechargingoperation, in the burn-in stress test.

In a typical example of word line controller circuit in accordance withthe third preferred embodiment shown in FIG. 8, in a similar manner tothe foregoing second embodiment, the output signal of the buffer 61 ofthe test mode discriminator circuit 60 will be input to the NAND gate 21to operate the test mode sequence circuit 20 in the burn-in stress test.The output signal of the inverter 62 of the test mode discriminatorcircuit 60 will be input to the NAND gate 72 to operate the user modesequence circuit 410 in the normal operation. In addition the low-levelpulse signal of the command latch circuit 100 will be fed to thecontroller circuit 200 directly as an internal active signal ACTV aswell as to the NAND gate 72. The output signal of the prechargingcontroller circuit 50 will also be input to the NAND gate 21.

The output signal of the precharging controller circuit 50, which is acircuit for accepting the precharging control signal TXPRE insynchronism with the falling edge of the external clock CLK, is the NANDgate output. The inverted signal of the precharging control signal TXPREand the output signal from the CLK falling edge detector circuit 40 areinput signals of the NAND gate. The CLK falling edge detector circuit 40will synchronize to the falling edge timing of the external clock CLK tooutput a high-level pulse having a predetermined width (in the exampleshown in FIG. 8, width of delayed period for three stages of invertergates). Therefore, if a low-level precharging control signal TXPREduring this high-level pulse is input, the precharging controllercircuit 50 will output a low-level pulse.

The operation of the controller circuit shown in FIG. 8 will bedescribed by referring to waveforms shown in FIG. 9. FIG. 9 showswaveforms in the burn-in stress test. The accessing command READ_CMDserved for a control command CMD will be input in synchronism with therising edge of a external clock CLK, while the precharging controllercircuit 50, which receives the low-level signal of the prechargingcontrol signal TXPRE in synchronism with the falling edge of theimmediately preceding external clock CLK, will output an internalprecharge signal PRE through the NAND gate 21 and the NAND gate 75 tothe controller circuit 200 to reset the word line activating signal WL.

Synchronized to the rising edge of an external clock CLK which follows,the accessing command READ_CMD will be input to the command latchcircuit 100 a predetermined period of time after the precharging controlsignal TXPRE to generate a low-level pulse signal served as an internalactive signal ACTV to be fed to the controller circuit 200 to set theword line activating signal WL.

More specifically, since the precharging control signal TXPRE is inputin synchronism with the falling edge of an external clock CLK, if thefalling edge timing is preceded an appropriately predetermined period oftime with respect to the immediately succeeding rising edge of theexternal clock CLK to synchronize the accessing command READ_CMD, theresetting period of the word line activating signal WL by the controllercircuit 200 in response to the internal precharge signal PRE will beconfigured as the least minimum precharging period, while the periodwhich follows will be served for the word line activating period,allowing the electrical stress when performing a burn-in stress test tobe applied at a maximum rate of duration in order to achieve a moreefficient burn-in stress test.

The precharging control command TXPRE to be input to the synchronoussemiconductor device that is the next generation SDRAM, in response tothe external signal input through a proprietary external terminal or anexisting external terminal will be supplied in synchronism with thefalling edge of the external clock CLK not used in the normal operation.The relationship between the rising edge and the falling edge may bearbitrarily configurable, and the resetting period of the word lineactivation signal WL in the inactivated state may be set an arbitraryperiod of time preceding a rising edge of the external clock CLK, whichtransit a word line activating period in the activated state. The wordline activating period in the burn-in stress test may be arbitrarilyconfigured while making use of the synchronization activating signal insynchronism with the external clock CLK in the normal operation of thesynchronous semiconductor device, a next generation SDRAM, allowing theword line activating period required in the burn-in stress test to beconfigured in an effective way. In addition, this may increase the rateof duration of the word line activation so as to shorten the period ofthe test. Furthermore, the timing of a falling edge with respect to arising edge of the external clock CLK and the input timing of theprecharging control signal TPRE may be readily adjusted for each test orduring a test in an arbitrary manner so as to always optimize the testefficiency.

It is to be noted here that the command latch circuit 100 is a latchunit; the CLK falling edge detector circuit 40, precharging controllercircuit 50 and the NAND gate 21 are an inactivating detector unit, theNAND gate 75 is an inactivating unit. Also the external clock CLK is asynchronization signal, the rising edge thereof is a firstsynchronization timing. Furthermore, the access command READ_CMD servedas a control command CMD is a synchronization activating signal. Thefalling edge of the external clock CLK is the second synchronizationtiming, the precharging control signal TXPRE is an inactivating signal,or first synchronization control signal.

In the normal operation, this preferred embodiment, which may act assimilar to the circuit in accordance with the foregoing secondembodiment, may measure the timing of t1 in the device, so that only oneaccessing command READ_CMD may invoke a complete operation for onecycle.

When conducting the burn-in stress test of the synchronous semiconductordevice in accordance with first through third preferred embodiments ashave been described above, since it is economical and effective to testa number of synchronous semiconductor devices in a test, an circuitboard of inspection bench in general is designed to accept a number ofsame synchronous semiconductor devices. The circuit board is in generalhoused in an environment test chamber such as a thermostatic chamber dueto the requirement of setting an inspection environment including thehumidity and the temperature. In this situation a variety of controlsignals, including commands such as the external clock CLK, controlcommand CMD, and precharging command PRE_CMD, and signals such as theprecharge control signals TPRE, TXPRE, the test mode input signal TTSTand the like may need to be individually supplied to each of thesynchronous semiconductor devices being subject to be tested. Inaddition, the influence including such as the load of wiring from thesignal supplier apparatus to the test chamber and the like should betaken into consideration. Therefore, the inspection system of thesynchronous semiconductor device in accordance with first through thirdpreferred embodiments of the present invention may be capable ofsupplying, at appropriate timings, such commands as the external clockCLK, control command CMD, precharging command PRE_CMD, and the like andsuch signals as precharge control signal TPRE, precharging controlsignal TXPRE, test mode input signal TTST and the like. Also theinspection system used may need to be ensured to have drivers capable offeeding signals to each of a number of synchronous semiconductor devicesmounted on an inspection circuit board in a positive and secure manner.More particularly, the inspection system needs to have output buffersthat can output binary values of high and low with a sufficient outputcurrent supply capacity as a driver, or output buffers that can outputternary values having a high impedance state, which system may have thedriving level and timings well controlled each other so as to outputpredetermined control signals based on the frequency of the externalclock CLK input and stored in advance, the input timing of the prechargecontrol signal TPRE and TXPRE compatible to the corresponding prechargeperiod, and the duty ratio of the external clock CLK or the commandsupplied from another configuration unit.

It is to be noted here that the external clock CLK used in first throughthird preferred embodiments are synchronization signals supplied from asynchronization signal supplier unit, the rising edge thereof is firstsynchronization timing, respectively.

In the first preferred embodiment described above, the accessing commandREAD_CMD served as a control command CMD is a synchronizationinactivating signal supplied from a synchronization inactivating signalsupplier unit.

In the second preferred embodiment described above, the accessingcommand READ_CMD served as a control command CMD is a synchronizationactivating signal supplied from a synchronization activating signalsupplier unit, while the precharge control signal TPRE is aninactivating signal supplied from an inactivating signal supplier unit.

In the third preferred embodiment described above, the accessing commandREAD_CMD served as a control command CMD is a synchronization activatingsignal supplied from a synchronization activating signal supplier unit,while the precharging control signal TXPRE is an inactivating signalsupplied from an inactivating signal supplier unit.

As can be appreciated from the above detailed description, in thesynchronous semiconductor device in accordance with first preferredembodiment of the present invention, the PRE circuit served forprecharging in a least minimum inactivated state will operate, then theACTV circuit served for accessing in an activated state will operatethereafter, due to the requirement of increasing the rate of duration ofthe activated state in the test mode sequence circuit 10 in order toconduct an effective burn-in stress test. As the least minimum inactiveperiod in this situation will be achieved by appropriately configuringthe measuring time tPR of the internal timer 13, a word line will beactivated after a least minimum precharging period required so that theelectrical stress may be applied at the maximum rate of time in aburn-in stress test, allowing a more effective burn-in stress test to becarried out.

In the synchronous semiconductor device in accordance with secondpreferred embodiment of the present invention, by setting the timing ofthe precharge control signal TPRE an appropriate period of time beforethe external clock CLK that is a synchronization signal for theaccessing command READ_CMD, the resetting period of the word lineactivating signal WL by the controller circuit 200 in response to theinternal precharge signal PRE will be configured as the least minimumprecharging period, while the period which follows will be served forthe word line activating period, allowing the electrical stress in aburn-in stress test to be applied at a maximum rate of duration toachieve a more efficient burn-in stress test.

Furthermore, in the synchronous semiconductor device in accordance withthird preferred embodiment of the present invention, by setting thetiming of falling edge of the external clock CLK an appropriate periodof time before the next rising edge of the external clock CLK thatsynchronizes the accessing command READ_CMD since the prechargingcontrol signal TXPRE is input in synchronism with the falling edge ofthe external clock CLK, then the resetting period of the word lineactivating signal WL by the controller circuit 200 in response to theinternal precharge signal PRE will be configured as the least minimumprecharging period, while the period which follows will be served forthe word line activating period, allowing the electrical stress in aburn-in stress test to be applied at a maximum rate of duration toachieve a more efficient burn-in stress test.

An inspection system for conducting a burn-in stress test of thesynchronous semiconductor devices in accordance with first through thirdpreferred embodiments of the present invention as have been describedabove may have output buffers that can output binary or ternary valueswith a sufficient output current supply capacity as a driver, and mayhave the driving level and timings well controlled each other so as tooutput predetermined control signals based on the frequency of theexternal clock CLK input and stored in advance, the input timing of theprecharge control signal TPRE and TXPRE compatible to the correspondingprecharge period, and the duty ratio of the external clock CLK or thecommand supplied from another configuration unit.

The present invention may be embodied in other specific forms withoutdeparting from the spirit or essential characteristics thereof.

For instance, in the second preferred embodiment, although an exemplarycircuit has been described by way of example in which the prechargecontrol signal TPRE may configure the least minimum precharging periodnecessary, by appropriately setting the input timing of the prechargecontrol signal TPRE, a low-level pulse that is to be input prior to theaccessing command READ_CMD that is a control command CMD, therelationship between the activating signal and the precharging signalmay be reversed. Namely, the state can be switched to “active” byreceiving a precharging command PRE_CMD synchronously with the risingedge timing of the external clock and then an appropriate period of timethereafter by inputting asynchronous activating signal. In the lattercase if the interval between a synchronization signal to an asynchronousactivating signal is appropriately adjusted, a word line will beactivated after a least minimum precharging period required so that theelectrical stress may be applied at the maximum rate of time in aburn-in stress test, allowing a more effective burn-in stress test to becarried out. It is to be noted here that the asynchronous activatingsignal designates to an activating signal, or a second asynchronouscontrol signal.

The word line activation period, namely the active state of the wordline, may be configured at an arbitrary timing by means of theactivating signal in correspondence with a signal external input via aproprietary external terminal or an existing external terminal.Therefore the word line activation period may be set after an arbitraryperiod of time following a rising edge of the external clock CLK, whichtransit a word line activating signal WL to the resetting period whichis in the inactivated state. The word line activating period in theburn-in stress test may be arbitrarily configured while making use ofthe precharging command PRE_CMD in synchronism with the external clockCLK in the normal operation of the synchronous semiconductor device, anext generation SDRAM, allowing the word line activating period requiredin the burn-in stress test to be configured in an effective way.Furthermore, this may increase the rate of duration of the word lineactivation so as to shorten the period of the test. In addition, theinput timing of the asynchronous activating signal may be readilyadjusted for each test or during a test in an arbitrary manner so as toalways optimize the test efficiency.

In the third preferred embodiment, although an exemplary circuit hasbeen described by way of example in which an accessing command READ_CMDserved as a control command CMD is input in synchronism with the risingedge of a external clock CLK while a low-level precharging controlsignal TXPRE is input in synchronism with the falling edge of theimmediately preceding external clock CLK, the relationship between theactivating signal and the precharging signal may be reversed. Namely,the accessing command READ_CMD may be input in synchronism with thefalling edge timing of an external clock CLK an appropriate period oftime after receiving a precharging command PRE_CMD in synchronism withthe rising edge timing of the external clock. In the latter case if theinterval between a precharging command PRE_CMD and an accessing commandREAD_CMD is appropriately adjusted, a word line will be activated aftera least minimum precharging period required so that the electricalstress may be applied at the maximum rate of time in a burn-in stresstest, allowing a more effective burn-in stress test to be carried out.It is to be noted here that the accessing command READ_CMD insynchronism with the falling edge timing of an external clock CLK is anactivating signal, or a second synchronization control signal.

The accessing command READ_CMD to be input to the synchronoussemiconductor device that is the next generation SDRAM, in response tothe external signal input through a proprietary external terminal or anexisting external terminal will be supplied in synchronism with thefalling edge of the external clock CLK not used in the normal operation.The relationship between the rising edge and the falling edge may bearbitrarily configurable, and the word line activation period may be setafter an arbitrary period of time following a rising edge of theexternal clock CLK, which transit a word line activating signal WL tothe resetting period which is in the inactivated state. The word lineactivating period in the burn-in stress test may be arbitrarilyconfigured while making use of the synchronization inactivating signalprecharging command PRE_CMD in synchronism with the external clock CLKin the normal operation of the synchronous semiconductor device, a nextgeneration SDRAM, allowing the word line activating period required inthe burn-in stress test to be configured in an effective way. Inaddition, this may increase the rate of duration of the word lineactivation so as to shorten the period of the test. Furthermore, thetiming of a falling edge with respect to a rising edge of the externalclock CLK and the input timing of the accessing command READ_CMD may bereadily adjusted for each test or during a test in an arbitrary mannerso as to always optimize the test efficiency.

In accordance with the present invention, a synchronous semiconductordevice and an inspection system thereof may be provided which mayimprove the efficiency of application of electrical stresses to thedevice in order to efficiently carry out a burn-in stress test, byreducing the duration of inactivated state to the least minimum in thetest to allow the duration of activated state to be arbitrarilyconfigurable so as to increase the rate of duration of active state.

The foregoing description of the preferred embodiment of the inventionhas been presented for purposes of illustration and description. It isnot intended to be exhaustive or to limit the invention to the preciseform disclosed, and modifications and variations are possible in lightof the above teachings or may be acquired from practice of theinvention. The embodiment chosen and described in order to explain theprinciples of the invention and its practical application to enable oneskilled in the art to utilize the invention in various embodiments andwith various modifications as are suited to the particular usecontemplated. It is intended that the scope of the invention be definedby the claims appended hereto, and their equivalent.

1. A synchronous semiconductor device having an inspection mode foralternately transiting between an activated state and an inactivatedstate in order to carry out a test in the activated state, comprising: alatch unit for latching a synchronization inactivating signal insynchronism with first synchronization timing in a synchronizationsignal; an activating detector unit for detecting an activating signal apredetermined period of time after the inactivated state; and anactivating unit for commanding the activated state based on theactivating signal detected by the activating detector unit.
 2. Asynchronous semiconductor device set forth in claim 1, wherein: theactivating detector unit is a delay unit for measuring a predetermineddelay time based on the signal generated from the synchronizationinactivating signal or based on the synchronization inactivating signalitself; and the activating signal is an input signal to the delay unit.3. A synchronous semiconductor device set forth in claim 2, wherein: thesynchronization inactivating signal is a synchronization activatingsignal in normal operation.
 4. A synchronous semiconductor device setforth in claim 1, wherein: the activating signal is a signal generatedbased on one or more second asynchronous control signals input from anexternal source.
 5. A synchronous semiconductor device set forth inclaim 1, wherein: the inactivating signal is generated based on one ormore second synchronous control signals input from an external sourceand in synchronism with second synchronization timing of thesynchronization signal.